Wheel cylinder for hydraulic brakes



Dec. 12, 1950 s. H. slME:

WHEEL CYLINDER EOE HYDRAULIC BRAKES 2 Sheets-Sheet 1 Filed April 28, 1947 gmc/MM SYLVAN H.SIME

Dec. l2, 1950 s. H. slME 2,533,902

WHEEL CYLINDER FDR HYDRAULIC BRAKES Filed April 2B, 1947 2 Sheets-Sheet 2 3 the central annular projections surrounded by recesses Ila.

A pair of projectable rods 24 extend outwardly from the outer ends of hydraulic pistons I2 and have their inner ends engaging a recessed central portion in the outer surface of pistons I2 and have their outer ends connected to the upper portions of brake-shoes 25 and 26 as shown in Figure 4. A brake-shoe retraction spring 21 has its outer ends connected with the upper portions of the brake-shoes 25 and 26 to resiliently urge said brake-shoes into retracted or normal position.

A brake drum 28 is adapted to have its inner periphery receive the outer periphery of brakeshoes 25 and 26 and to completely surround said brake-shoes 25 and 26. The brake drum 28 is fixed to an automobile wheel (not shown) and rotates therewith.

A backing plate 29 is rigidly xed to a nonrotatable portion of the automobile as by capscrews through the apertures 29a. The wheel cylinder A is horizontally fixed on the upper portion of said backing plate 29 and has its projectable rods 24 pivotally attached to the upper portion of brake-shoes 25 and 26. The lower portion of brake-shoes 25 and 26 are pivotally connected with the outer ends of links 30 the inner ends of links 36 being mounted on a pin 3| which is rigidly connected with the lower portion of said backing plate.

Operation In the operation of a standard wheel cylinder as is now in use the fluid under pressure from the master cylinder (not shown) enters as through the inlet I to ilow directly into the piston cylinders II to operate the pistons I2 and move the projectable rods 24 and the brake-shoes 25 and 26 outwardly to engage against the inner peripheral surface of the brake drum 28. When the automobile wheel is rotating in the direction indicated by the arrow in Figure 4 brakeshoe 25 will be the primary shoe and brake-shoe 26 becomes the secondary shoe. Due to the frictional force exerted between the shoe 25 and the drum 28 the rotation of the drum will tend to "drag the upper portion of the brake-shoe 25 more tightly against the drum 28 while the same rotation will tend to push the upper portion of the secondary shoe 26 away from the drum 26. The links 30 as shown in Figure 4 serve to equalize the pressure between the primary and the secondary shoes 25 and 2G in that the lower end of secondary shoe 26 is mounted in floating relationship in relation to the drum 28 and thus the rotation of the drum 28 will tend to drag the lower end of secondary shoe 26 against it increasing the pressure thereon and more or less equally distributing the force exerted between the two shoes 25 and 26. This linkage arrangement or some other means for equalizing the pressure exerted by the two shoes is in use on most of the modern cars today and does not constitute a pair of my invention.

The mechanism of mywheel cylinder A is shown in extreme brake-operating position in Figures 1 and 2. My hydraulic system is bled in the same manner as conventional hydraulic systems. The bleeder holes 2l are opened and hydraulic fluid is pumping into the wheel cylinder from the master cylinder (not shown) by pumping the brake pedal (not shown) until all the air in the system has been displaced by fluid. The bleeder holes 2I are then plugged.

To initially adjust the brakes to a predetermined clearance between the shoes 25 and 26 and the drum 28, the brake pedal (not shown) is pushed down to operate the `master cylinder (not shown). Hydraulic fluid is thus forced under pressure into the central inlet passage I5 and from there outwardly into the two branch inlets I6 and thus into the inner ends of the valve cylinders I'l. The hydraulic pressure projects the valve pistons 22 outwardly to open the by-pass passages I8 and permit fluid to flow under pressure from the master cylinder outwardly into said passages I8 and said openings 20 into the inner ends of the main cylinders II. The fluid under pressure exerts force on the inner ends of the brake-actuating pistons I2 and moves said pistons I2 outwardly to forcibly project said brake shoes 25 and 2B against the brake drum 28.

When the by-pass passages I8 are opened the hydraulic pressure in the inner ends of said valve cylinders Il will ultimately become equal to the hydraulic pressure in the inner ends of main cylinders II. However, as the pressure on the brake pedal is being initially increased, the hydraulic pressure within the valve cylinders I'I will be greater than the hydraulic pressure in the main cylinders I I and will maintain the valve piston in extreme projected position by maintaining a greater pressure against the inner ends of said valve pistons 22 than in the main cylinders II. But as soon as the pressure on the brake pedal is stabilized and is no longer being increased, but merely held in brake-operating position, the hydraulic pressure Within the main cylinders I I and the valve cylinders I1 will be quickly equalized. Since the hydraulic pressure against the valve pistons 22 must be equal to the hydraulic pressure within cylinders II plus the force exerted by the springs I4, as soon as the hydraulic pressures in the cylinders II and I1 become equal, the springs I4 will operate to retract the valve pistons 22 and close off by-pass passages I8, trapping within the inner ends of main cylinders II all of the fluid which has flowed therein. The pistons 22 will continue to move inwardly until the hydraulic pressure against the inner ends thereof is equal to the sum total of the hydraulic pressure within the inner ends of main cylinders II plus the force exerted by the springs I4.

When the brake pedal is released the valve pistons 22 will move inwardly into extreme retracted position, where the recesses IIa will receive sealer anges 23a and permit the central -portions of the sealer caps 23 to firmly seat themselves against the central annular portions surrounded by the recesses Ila. It will be seen that the retraction of the valve pistons 22 after the Y release of the brake pedal will permit the brakeactuating pistons I2 to be retracted a proportionate distance and permit a predetermined normal clearance between the brake-shoes 25 and 26 and the brake drum 28. The brakes are now in perfect adjustment and will remain constantly in adjustment until the brake linings are completely worn out and have to be replaced. The volumes of fluid retained within the main cylinders I I will remain constant until wear occurs on the brake-shoes 25 and 26, at which time the said volumes will be increased to maintain a predetermined clearance between brake-shoes 25 and 26 and brake drum 28, as will be described later.

The two principal factors which determine the clearance between the brake-shoes and the brake drum are the diameter of the valve pistons 22 with 5 felation to the diameter of the hydraulic pistons l2 and the distance which the valve pistons move vafter release of the brake pedal, or in other words, the volume of fluid which the outer ends of the valve pistons 22 displace within the inner ends of the main cylinders Il during their operating stroke. These portions may ci Acourse be aibv justed to maintain any Idesired predetermined` adjustment of the brake-shoes 25 and 26 'rela-l tive to the brake drum 28.

Often in the normal operation of the brakes the small pistons 22 will serve entirely to project the brake-shoes 25 and 2B against 'the brake drum 28 and will not move out a su-mcient distance to open by-.pass passages i8. This is true because the brake-shoes as now manufactured wear Vrelatively slowly and .it will not be necessary to increase the volume of ilu'id retained Vin the inner ends of main cylinders Il until wear occurs on said brake-shoes. Due to the inherent slight compressibility of the brake-shoes and linkage between them and pistons Ll2 it lis apparent that in cases of .great emergency, when extreme sudden pressures are vapplied to the valve -pistons 22, the said pistons .22 will be projected outwardly a sufcient distance to open the by-pass .passages i8 rand permit a slight amount of uid to flow into the .inner endsof the main cylinders lil, but normally the displacement of the outer ends of the valve pistons into the main cylinders I I will be sullcient to operate the brakes until wear occurs on the brake-shoes 25 and 26.

`As the brake-shoes 25 and 26 wear, the respective volumes of fluid retained within the inner ends of the main cylinders Il must vbe increased to maintain the predetermined spaced `relation between brake-shoes .25 and 26 and brake drum 28. Obviously, when the prior application 'of the brakes has produced wear on the brake-shoes y2li and 25, the valve .pistons 22 will have to move outwardly va greater distance in order to apply the brakes, and in the event that there has been sunicient wear to permit said :pistons 22 toopen `luy-.pass pasages I8 a small amount of .iiuidrwill der A operates except that wheel cylinder Bcom- V within a brake assembly lis to convertbothibralie- Y shoes into primary shoes. With :the brake ldrum 34 rotating inthe direction of vthe farrow shown in Figure 5 both shoes 35 will 'be vprimary:shoes` and the rotation .ofthe drum will'tend to drag the shoes `into engagement with:the1drum.

It will be seen vfrom the Tforegoing descisiiztion that with my mechanism, yregardless of the wear on the brakeshoesfthe actuating stroke in applythe brakes is always nonst'ant, as lis :the 'nonmal spaced .relation between thefshoes fand the drum. As the brake-shoes wear, the normal retracted position of the pistons l2 changes accordingly as the volume of uid retained in the inner ends ofthe cylinders Il increases to compensate for said brake-shoe wear. The resilient connection between the valve Ypistons 22 and .said actuating pistons i2 permits the spaced relation therebetween to -be varied both during `operation andin the normal retracted position thereof. By providing brakes which `are always maintained in constant adjustment it will be seen that vthe use of larger wheel cylinders Ais possible `because the necessity of a safety reserve in the allowable foot-pedal travel to provide for wear on the wheel lcylinders relative to the size of the master cylinder to increase mechanical advantage is eliminated bythe fact that there is a denite limitation on the allowable footpedal travel and the fact that there must-be some provision to perm-it wear on the shoes `so that even if the brakes are not in perfect adjustment lthere will be suilicient pedal to apply the brakes. With my improved construction the wear on the shoes will be compensated for by my yvalve adjustment mechanism, 'which increases the normal residual volume of iluid retained in the cyli-nders H as wear foccurs. Also the laborious manual adjustments which must be 'made 'from time :to time on conventional hydraulica'lly operated 'brakes is eliminated with my improved construction, saving not only laborl costs r`but also 4material 'costs in manufacturing the manual adjustment mechanism. A very im' portant safety factor is provided also by elimihating `the chance for human error in neglecting' to have the necessary manual adjustments made' or `in making poor adjustment in 'the conven'.

tional systems.

rIt will 'of `course "be understood that my invention or the working mechanism herein disclosed is Vvby no means limited 5to brake-operating :de vices, but is equally applicable to other mechanisms when it is desired to maintain a constant predetermined actuating stroke and spaced relationship between a 'project'able element 'and a' cooperating 'element related thereto.

It will, 'o'f course, be understood that various changes may 'be made in the form, details, .1ar-

rangement and proportions of .the parts with# out departing from the scope or my invention.

What I claim '11. .A uid koperated system for projecting .a normally retracted projectable element against an .element adapted to cooperate therewith, comi .prising a fluid coniining cylinder, ,an actuating piston working within ,said cylinder and adapted to be connected to a projectable element, means defining a passage for connecting said cylinder V.witha controlled source of fluid under pressure, a duid Vdisplacing element projectable into said cylinder when subjected to iiuid jpressure from said source to displace a substantially predetermined volume of fluid in lsaid cylinder, and a valve element operative 4in said passage to Anor-- lm'ally close the same vbut opening Awhen more than vsaid vpredetermined volume 4of iluid 'has vbeen displaced, whereby a predetermined actuat ing stroke of said actuating piston and spaced relation between the projectable 4element `in normal position and the element adapted to cooperate are maintained.

12. AA "uid operated system for projecting a normally retracted projectable element Yagainst fa. -cooperating Ielement, 4comprising a iiuid foonc5 cylinder, van actuating pistoni working within said cylinder and adapted to be connected to a projectable element, means defining a passage for connecting said cylinder with a controlled source of fluid under pressure, a, fluid displacing element projectable into said cylinder when subjected to fluid pressure from said source to displace a substantially predetermined volume of fluid in said cylinder and project said projectable element a predetermined distance toward the element adapted to cooperate therewith, and a valve element connected withsaid uid displacing element for movement therewith and operative in said passage to normally close the same but opening when more than said predetermined volume of fluid has been displaced by said displacing element to permit the volume of uuid in said cylinder to be increased to compensate for weanbetween said projectable element and said cooperating element,iwhereby a predetermined actuating stroke of said actuating piston and spaced relation between the projectable element in normal position and the element adapted to cooperate therewith are maintained.

3. A hydraulically operated system for projecting a normally retracted projectable element against a cooperating element, comprising a fluid confining cylinder, an actuating piston working within said clyinder and adapted to be connected to a projectable element, means defining a passage for connecting said cylinder with a controlled source of hydraulic fluid under pressure, a fluid displacing element projectable into said cylinder when subjected to fluid pressure from said source to displace a substantially predetermined volume of fluid in said cylinder and project said projectable element a predetermined distance toward the element adapted to cooperate therewith, a valve element connected with said fluid displacing element for movement therewith and operative in said passage to normally close the same but opening when more than said predetermined volume of fluid has been displaced by said displacing element to permit additional fluid under pressure from said source to flow into said cylinder, and a resilient member interposed between said fluid displacing element and said actuating piston'to urge said displaceable element inwardly and close ofi said valve to retain an increased volume of 'residual fuid within said cylinder to compensate for wear between said projectable element and the element adapted to cooperate therewith, whereby a predetermined actuating stroke of said piston and spaced relation between the' projectable element in normal position and said cooperating element are maintained.

4. A hydraulically operated system for projecting a normally retracted proiectable element against a coopera-ting element, comprising a fluid confining cylinder, an actuating piston working within said cylinder and adapted to be connected to a projectable element, means defining a passage for connecting said cylinder with a controlled source or hydraulic fluid under pressure, a piston valve working in said passage and responsive for operation to fluid supplied under pressure frcm said source and to have a portion thereof projectable into said cylinder to displace a predetermined volume of fluid therein, said valve normally closing said passage but opening the same when more than said predetermined volume of fiuid has been displaced by said piston valve to permit additional fluid under pressure from said source to flowl into saidcylinder and means forretracting said piston valve to close said passage whereby an increased volume of residual fiuid is retained within said cylinder to compensate for the wearing off of the cooperating surfaces of said projectable element and the element Vadapted to cooperate therewith, whereby a predetermined actuating stroke of said piston and spaced relation between the projectable element in normal position and said cooperating element are maintained.

. 5 A hydraulically operated system for projecting a normally retracted projectable element against a cooperating element, comprising -a fuid confining cylinder, an actuating pis ton working within said cylinder and adapted to be connected to a projectable element, means defining a passage for connecting said cylinder with a controlled source of hydraulic fiuid under pressure, a piston valve working in said passage and responsive for operation to fluids supplied under pressure from said source and to have a portion thereof projectable into said cylinder to displace a predetermined volume of fluid therein, said valve normally closing said passage but opening the same when more than said predetermined volume of fluid has been displaced by said piston valve to permit additional fluid under pressure from said source to flow into said cylinder and a resilient member interposed between said piston valve and said actuating piston to urge said piston valve inwardly and close off said passage to increase the volume of residual fluid retained within said cylinder to compensate for the wearing off of the cooperative surfaces of said projectable element and element adapted to cooperate therewith, whereby a predetermined actuating stroke of said piston and spaced relation between the projectable element in normal position and said cooperating element are maintained.

' 6. A fluid operating mechanism comprising a cylinder, an actuating piston working in said cylinder, means defining a passage for connecting one end of said cylinder with a controlled source of fluid under pressure, means defining a Valve chamber one end of which is interposed into said passage, said valve chamber having its other end portion communicating with said end of said cylinder, a piston Valve working in said valve chamber to normally seal off said passage and being responsive for operation to fluid supplied under pressure from said source to have one end thereof projectable into said cylinder to displace a predetermined volume of fluid therein and having the other end adapted to open said passage when said predetermined volume of fluid has been displaced in said cylinder and permit additional fluid to be supplied to said cylinder under pres--l sure from said source, and a resilient member interposed between said piston valve and said actuating piston to close off said passage and retain an increased Volume of residual fluid within said cylinder.

7. A fluid operating mechanism comprising a wheel cylinder, an actuating piston working in said cylinder and adapted to be connected to a normally retracted projectable element of the type having means associated therewith for retracting the same, means defining a valve chamber having one end communicating with said end of said cylinder, means dening a passage for connecting the other end of said chamber with a controlled source of fluid under pressure, means affording lateral by-pass communication between an intermediate portion of said valve chamber and said end of said cylinder, a piston valve working in said valve chamber in sealed relation thereto to normally seal off communication between said passage and said by-pass means and responsive for operation to fluid pressure from said source against one end of said piston valve to move said piston valve and normally project the outer end thereof a substantially predetermined distance into said cylinder to displace a substantially predetermined volume of fluid in said cylinder and project said element a predetermined distance, said piston valve permitting uid under pressure from said source to ow into said cylinder through said by-pass means only after said piston valve has been moved more than said predetermined distance, and resilient means interposed between said actuating piston and said piston valve to close off said by-pass means and retain an increased volume of residual uid within said cylinder, said element retraction means supplying return pressure to aid said resilient member in seating said piston valve against said second mentioned end of said valve chamber.

SYLVAN H. SIME.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Certicate of 'Correction Patent No. 2,533,902 December 12, 1950 SYLVAN H. SIME It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 64, for the Word pair read part; column 6, line 71, after operate7 insert therewith;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent O'lice. Signed and sealed this 13th day of February, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assz'stapt Oommz'ssz'oner of Patents. 

